Timing is everything.

Opportunity does not knock twice.

These trite phrases have an inordinate amount of truth to them, especially when they are applied to political life — now as much as ever.

Most Americans look at the condition of the nation’s political leadership today with disbelief.

Not since the times of Nixonian cover-ups or Clintonian degradations has there been such head-shaking about the state of the presidency.

Not since the days of George McGovern or the chaotic 1968 Democratic Convention in Chicago has there been such head-shaking about the leftist tilt of the Democratic Party.

Donald Trump has turned the presidency into an extrusion of childish tantrums, superficial and dishonest claims, and consistent inconsistency.

Among the leading Democratic candidates to replace him, Sens. Elizabeth Warren, D-Mass., and Bernie Sanders, I-Vt., revel in rolling out proposals to the left of the socialist movements of Europe. There is no limit to their largesse or to their desire to determine how we other Americans should live our lives.

Former Vice President Joe Biden, who might claim to be the only rational adult in the contest, is constrained by his own failings.

Ironically, Biden’s ability to remain viable, despite those obvious weaknesses, underlines how the current moment provides a political chance of a lifetime.

Trump, Warren and Sanders represent — albeit in very different ways — those who shout from the corners of the political process.

They do not, however, represent a majority of Americans, who are simply working to get through their day, make ends meet, raise their family and pursue the opportunities this nation provides.

There is a real thirst amongst the vast majority of people — those who are not activists or extremists — for someone like Biden.

Someone decent, substantive, rational and non-extreme, who reflects their values. Someone who understands the respect that America has earned over the years across the world. Someone who is a plain nice person with depth and compassion, who sees and understands the values that make America unique.

Unfortunately for Joe Biden, it is probably not Joe Biden.

This is not because he does not have the character and purpose to fill this void but because he simply is not going to make it to the finish-line of the Democratic Party’s nomination process.

Good people are at a considerable disadvantage in this process.

Social media has taken over.

It gives unusual and unfettered power to extremists — the shouters, the conspiracy theorists and those least likely to tolerate anyone with whom they disagree.

Warren and Sanders are perfect social media candidates.

They exude extremism in policy. Their style is to loudly proclaim their righteousness as they embrace intolerance.

Biden is simply out of step with the nature of the current Democratic Party, which, by the way, is out of step with America.

Trump is the presumed 2020 nominee of the Republican Party.

The Republican Party leadership has essentially declared there will be no nominating process that tolerates substantive dissent. State after state is voiding its primary elections to more easily anoint the president.

The Republican Party wishes to have no debate over Trump’s style, character, actions or eccentricities. Such a discussion would, it is presumed, be detrimental to his reelection hopes.

The primary goal of the Republican Party leadership right now is to retain the White House.

But most Americans actually do not see things the same way as the Republican Party leadership.

They wonder about the president’s inconsistencies, his immaturity, his bullying, his inaccuracies and his incessant narcissism.

His polling numbers are at near-historic lows. Even many voters who lean to the right find it difficult to justify supporting him, other than on the basis that he is the least-bad option available.

The question which is most often heard, once one tunes out the activist news media, is: How do we, the nation, get something better?

So far, no-one better is willing to step forward.

The Republican Senate, where it would seem that such a person might be in residence, is in hiding. So are the Republican governors.

They fear the voices of social media and the hatred that would be spewed their way if they were to step up and challenge the president.

They do not want to put their political future at risk on a mission that carries such a small chance of success. They are biding their time, awaiting the passing of Trump’s time.

On the Democratic side, the party has jumped the rails.

Its dominant ideology no longer tolerates the idea that our market economy, which has created the greatest economic success in history and is envied around the world, is working.

It would be difficult for a candidate who is not a true believer in absurdities like the Green New Deal or Medicare for All to out-shout Warren and Sanders.

There are some thoughtful, rational and constructive people in the Democratic race, such as Sens. Amy Klobuchar, D-Minn., and Michael Bennett, D-Colo., but they can get no traction.

The need for a real political leader remains.

Someone has the opportunity of a political lifetime.

A person of accomplishment should step up and run on a theme that encompasses the general goodwill and values of most Americans.

It is unlikely that someone other than Trump will be nominated by the Republican Party.

But in 1964, when then-Sen. Barry Goldwater of Arizona was battling then-New York Gov. Nelson Rockefeller for the Republican nomination, there was also a level of frustration with the candidates.

Henry Cabot Lodge won on a write-in campaign in the New Hampshire primary, even while serving as U.S. ambassador to South Vietnam. This turned out to be a stark predictor of the electorate’s reservations. Although Goldwater received the nomination, he was trounced in the general election by President Lyndon Johnson.

It would be welcome to many Americans if, right now, someone of stature within the Republican Party would stand up and call the nation to a higher purpose.

It would also be nice if someone in the Democratic Party would step into the shoes of Biden, and carry forth his message of being rational, thoughtful and substantive.

In fact, he or she should bring back the policy approaches favored by President Clinton, 2000 nominee Al Gore and even to some extent President Obama. He or she should push back on this drive toward socialism.

Maybe then they could speak over the excesses of social media.

Such an individual would have a message that is thirsted for by a huge number of Americans. Voters really do want to be led by someone whom they can respect and who carries the torch of uniqueness that is America.

This is an unusual time, when there is the need for a person of strength to stand up and go against the current.

It is a chance to make a dramatic difference in the direction of the country; to lead, and to embrace our country’s greatness of purpose; to be, you might say, a profile in courage.

Republican Judd Gregg is a former governor and three-term senator from New Hampshire who served as chairman and ranking member of the Senate Budget Committee, and as ranking member of the Senate Appropriations Foreign Operations subcommittee. This column first ran in The Hill and appears courtesy of the writer.